We develop a virial analysis of self-gravitating spheroids and predict the effects of Universe expansion on the stability of these systems. We find that as the pressure and temperature of the Universe decreases in time, the critical mass that is unstable to collapse decreases. The largest self-gravitating body is the Universe and we show that the critical mass at the time of element formation corresponds with the present estimate of the mass of the Universe. Subsequently, as the temperature falls further, lower mass systems will collapse and form the next dominant form of self-gravitating bodies, i.e. the large-scale structures and clusters of the observable galaxies. Subsequently, as these clusters cool with Universe expansion, the next largest mass systems will condense out, namely the galaxies. Recent observations have shown that the Universe has seen new groups of galaxies being formed throughout its history. It appears to be populated by dominant species of galaxies at different times. Our analysis shows that the size and age of these galaxies is comprehended through our critical mass argument.

This research was awarded an Honorable Mention in the 1992 Gravity Research Foundation essay competition.